A group of bolts are suppled into a placing surface of a tray, an isolated bolt is searched for by a visual sensor, and its deviation from a standard position at the time of teaching is determined. The isolated bolt is picked up by a robot that has been taught how to pick up an isolated bolt laying in a standard position. The position of the robot's hand is corrected according to the deviation from the standard position before the robot attempts to pick up the located isolated bolt. If no isolated bolt is found, a shaking device 1 is operated to loosen the piled-up bolts, and a new isolated bolt is again searched for by the visual sensor. The isolated bolt, if found, is picked up. The picking-up operation may be performed by searching for an isolated small set of bolts using a three-dimensional visual sensor. The oscillating excitation can also be provided by a robot. Also, the piled-up bolts may be loosened or disentangled using a robot equipped with a tool for leveling the pile of bolts or by using a gas jet.